#include<stdio.h>
#include<iostream>
#include<algorithm>
#include<vector>
#include<queue>
#define int long long
using namespace std;
const int MAXN=1e6+10;
int T,n,m,c,a[MAXN],b[MAXN],cost,cnt;
priority_queue <int,vector<int>,greater<int>> q;
inline void work()
{
    while(!q.empty()) q.pop();
    cost=cnt=0;cin>>n>>m>>c;
    for(int i=1;i<=n;++i) cin>>a[i];
    for(int i=1;i<=n;++i)
    {
        cin>>b[i],b[i]=min(b[i],a[i]);
        while(!q.empty()&&m<b[i])
        {
            int cur=b[i]-m,x=q.top();
            if(cur<=x) break;
            else cost+=x,m+=(x+1),q.pop();
        }
        if(m<b[i])
        {
            int cur=b[i]-m,s=min(cur/(c+1),cnt);
            cost+=s*c,m+=s*(c+1),cnt-=s;
        }
        int use=min(m,b[i]),now=a[i]-use;
        m-=use,cost+=now,m+=now/c;
        int num=c-now%c;
        if(num<=use) q.push(num),cnt+=(use-num)/c;
    }
    cout<<cost<<'\n';return ;
}
signed main()
{
    // freopen("coupon6.in","r",stdin);
    // freopen("out.out","w",stdout);
    cin.tie(0),cout.tie(0);
    ios::sync_with_stdio(0);
    cin>>T;while(T--) work();return 0;   
}